Is the render output linear color or 2.2 gamma?
The gamma of the output image depends on what the image format supports. Generally, output to PNG or JPG will result in a non-linear gamma correction (2.2). Usage of the OpenEXR format supports linear colour space, and you would keep your 1.0 gamma value.

Additional info: http://wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.64/Color_Management